Bob - Looking at the photo I see the holes for the pins in the center sill beams. If you put two pins in each in stead of one it will be considerably stronger with out adding the steel bar. The single pin acts as a pivot in the joint, two pins act as a lock.
If you are going to add the steel bar as described, I would assume you are going to notch the needle beams to allow the bar to sit flat on the center sill beams. And with that you might consider drilling and tapping the steel bar at the truck pins and slipping the bar below the boss for the truck mount.
Yeah, I know … “Where were you when the paper was blank?”
